(a) At the Trial. A juror may not testify as a witness before the other jurors at the trial. If a juror is called to testify, the court must give a party an opportunity to object outside the jury's presence.

(b) During an Inquiry into the Validity of a Verdict or Indictment.

(1) Prohibited Testimony or Other Evidence. During an inquiry into the validity of a verdict or indictment, a juror may not testify about any statement made or incident that occurred during the jury's deliberations; the effect of anything on that juror's or another juror's vote; or any juror's mental processes concerning the verdict or indictment. The court may not receive a juror's affidavit or evidence of a juror's statement on these matters.

Subdivision (a) prohibits a juror from testifying in a case in which that juror is sitting. Many of the practical and theoretical problems that are present when a judge testifies are also present when a juror does so. The impartiality with which the trier of fact should consider evidence is immeasurably damaged whenever a juror presents evidence for one of the parties to a lawsuit.

Subdivision (b) prohibits a juror from testifying as to the mental processes inherent in arriving at a verdict but allows jurors to testify as to whether outside influences were brought to bear upon a juror, or whether the verdict was arrived at by chance. Subdivision (b) was amended, effective March 1, 2008, to allow juror testimony about mistakes in entering the verdict on the verdict form.

The rationale of this rule is to further free deliberation in the jury room by protecting from disclosure the manner in which a verdict was reached, and to promote finality of verdicts. At the same time considerations must be given to the arrival of a just result in each particular case. Where a verdict is reached because of extraneous, prejudicial information or outside influence, much of the reason for disallowing a juror to testify disappears, and the balance is weighted in favor of obtaining justice in the individual case. Justice also requires disclosure whenever a verdict is arrived at by chance, including a "quotient" verdict, in which the jurors agree in advance to be bound. Although the view has been criticized, it is felt that reaching a verdict by chance is an extreme irregularity which replaces deliberation rather than being a part of it and, as such, should be disclosed.

Rule 606 was amended, effective March 1, 1990. The amendments are technical in nature and no substantive change is intended.

Rule 606 was amended, effective March 1, 2014, in response to the December 1, 2011, revision of the Federal Rules of Evidence. The language and organization of the rule were changed to make the rule more easily understood and to make style and terminology consistent throughout the rules. There is no intent to change any result in any ruling on evidence admissibility.